Pressure sensitive adhesive sheet for batteries and lithium-ion battery

ABSTRACT

[Problems] Objects include providing a pressure sensitive adhesive sheet for batteries that is excellent in the insulation properties even after heated to high temperatures and also excellent in the insulation properties even when immersed in an electrolyte solution for a long time and then heated to high temperatures and also providing a lithium-ion battery in which the pressure sensitive adhesive sheet for batteries is used. 
     [Solution] A pressure sensitive adhesive sheet for batteries ( 1 ), comprising: a base material ( 11 ); a hard coat layer ( 12 ) provided at one side of the base material ( 11 ); and a pressure sensitive adhesive layer ( 13 ) provided at a side of the hard coat layer ( 13 ) opposite to the base material ( 11 ), the hard coat layer ( 12 ) being formed of a composition for hard coat layer that contains a metal oxide sol, the metal oxide sol being a sol of a metal oxide that has insulation properties.

TECHNICAL FIELD

The present invention relates to a pressure sensitive adhesive sheet for batteries and a lithium-ion battery manufactured using the pressure sensitive adhesive sheet for batteries.

BACKGROUND ART

In some batteries, a strip-like laminate is housed therein in a state in which the laminate is wound up. The laminate is formed by laminating a positive electrode, a negative electrode, and a separator located between the positive and negative electrodes. The positive and negative electrodes are connected to respective electrode lead-out tabs of conductors, which electrically connect the positive and negative electrodes respectively to a positive electrode terminal and a negative electrode terminal of the battery.

A pressure sensitive adhesive tape may be used as a stopper for the above wound-up laminate and/or used for fixation of the electrode lead-out tabs to the electrodes. Patent Literature 1 and Patent Literature 2 disclose such pressure sensitive adhesive tapes. These pressure sensitive adhesive tapes each comprise a base material and a pressure sensitive adhesive layer provided on one surface of the base material.

PRIOR ART LITERATURE Patent Literature

[Patent Literature 1] JP5639733B

[Patent Literature 2] JP2011-138632A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

A pressure sensitive adhesive tape used inside a battery may be in contact with an electrolyte solution which fills the battery and may also be exposed to heat generated, such as during charge and discharge of the battery. Particularly in recent years, development of compact and high performance batteries has been progressed, and the pressure sensitive adhesive tape used inside the batteries will be exposed to more severe conditions.

The base material which constitutes the pressure sensitive adhesive tape used inside a battery is generally made of a material having insulation properties, but if such a base material is exposed to high temperatures, then carbonization and/or burning/decomposition (which may be referred to as “carbonization and the like,” hereinafter) may occur to alter the entire base material to a conductor. In this case, the pressure sensitive adhesive tape will exhibit conductivity and, in a battery in which the pressure sensitive adhesive tape is used, short circuit and/or thermal runaway may occur due to the pressure sensitive adhesive tape to cause a serious accident. The pressure sensitive adhesive tape used inside a battery is therefore required to maintain the insulation properties even when exposed to high temperatures. In addition, the pressure sensitive adhesive tape used inside a battery may be immersed in an electrolyte solution and is therefore required to maintain the insulation properties even when immersed in the electrolyte solution for a long time.

The present invention has been made in consideration of such actual circumstances and an object of the present invention is to provide a pressure sensitive adhesive sheet for batteries that is excellent in the insulation properties even after heated to high temperatures and also excellent in the insulation properties even when immersed in an electrolyte solution for a long time and then heated to high temperatures. Another object of the present invention is to provide a lithium-ion battery in which the pressure sensitive adhesive sheet for batteries is used.

Means for Solving the Problems

To achieve the above objects, first, the present invention provides a pressure sensitive adhesive sheet for batteries, comprising: a base material; a hard coat layer provided at one side of the base material; and a pressure sensitive adhesive layer provided at a side of the hard coat layer opposite to the base material, the hard coat layer being formed of a composition for hard coat layer that contains a metal oxide sol, the metal oxide sol being a sol of a metal oxide that has insulation properties (Invention 1). As used in the present description, the term “sheet” encompasses the concept of a tape. As used in the present description, the hard coat layer refers to a layer that is formed of a harder material than the base material, and does not mean a layer that exists as the outermost layer of a film.

The pressure sensitive adhesive sheet for batteries according to the above invention (Invention 1) has the hard coat layer formed of the composition for hard coat layer which contains a sol of a metal oxide having insulation properties (i.e., the hard coat layer contains metal oxide particles having insulation properties), and is thereby excellent in the insulation properties when heated to high temperatures. Moreover, the pressure sensitive adhesive sheet for batteries is excellent in the insulation properties even when immersed in an electrolyte solution for a long time and then heated to high temperatures because the above metal oxide particles are less likely to escape from the hard coat layer.

In the above invention (Invention 1), the metal oxide sol may preferably be at least one type selected from the group consisting of an alumina sol, zirconia sol, and magnesia sol (Invention 2).

In the above invention (Invention 1, 2), the composition for hard coat layer may preferably contain the metal oxide sol and an active energy ray-curable component (Invention 3).

In the above invention (Invention 1 to 3), the hard coat layer may preferably contain 0.01 cm³/m² or more and 7 cm³/m² or less of metal oxide particles originated from the metal oxide sol (Invention 4).

Second, the present invention provides a lithium-ion battery wherein two or more conductors are fixed in a state in which the two or more conductors are in contact with each other in the battery using the above pressure sensitive adhesive sheet for batteries (Invention 1 to 4) (Invention 5).

Advantageous Effect of the Invention

According to the pressure sensitive adhesive sheet for batteries and the lithium-ion battery of the present invention, the pressure sensitive adhesive sheet for batteries is excellent in the insulation properties when heated to high temperatures and also excellent in the insulation properties even when immersed in an electrolyte solution for a long time and then heated to high temperatures.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a pressure sensitive adhesive sheet for batteries according to an embodiment of the present invention.

FIG. 2 is a partially cross-sectional, exploded perspective view of a lithium-ion battery according to an embodiment of the present invention.

FIG. 3 is a developed, perspective view of an electrode body of the lithium-ion battery according to an embodiment of the present invention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described.

<Pressure Sensitive Adhesive Sheet for Batteries>

As illustrated in FIG. 1, a pressure sensitive adhesive sheet for batteries 1 according to an embodiment of the present invention may be constituted of a base material 11, a hard coat layer 12 provided at one side of the base material 11, a pressure sensitive adhesive layer 13 provided at a side of the hard coat layer 12 opposite to the base material 11, and a release sheet 14 provided at a side of the pressure sensitive adhesive layer 13 opposite to the hard coat layer 12.

Here, the “pressure sensitive adhesive sheet for batteries” in the present description is a pressure sensitive adhesive sheet used at a site at which there is a possibility of contact with an electrolyte solution when manufacturing a battery, may preferably be a pressure sensitive adhesive sheet used inside a battery, and may also be a pressure sensitive adhesive sheet for battery interior. The battery may preferably be a nonaqueous battery. Accordingly, the electrolyte solution used in the battery may preferably be a nonaqueous electrolyte solution. The pressure sensitive adhesive sheet for batteries in the present description may preferably be a pressure sensitive adhesive sheet that is attached to a site at which there is a possibility of immersion in an electrolyte solution inside a nonaqueous battery or a site at which there is a possibility of contact with an electrolyte solution. A lithium-ion battery may be particularly preferred as the nonaqueous battery.

The hard coat layer 12 of the pressure sensitive adhesive sheet for batteries 1 according to the present embodiment is formed of a composition for hard coat layer that contains a metal oxide sol and the metal oxide sol is a sol of a metal oxide that has insulation properties. That is, the hard coat layer 12 of the pressure sensitive adhesive sheet for batteries 1 according to the present embodiment contains metal oxide particles that are originated from the metal oxide sol and have insulation properties. The pressure sensitive adhesive sheet for batteries 1 according to the present embodiment is excellent in the insulation properties in an ordinary state because the pressure sensitive adhesive sheet for batteries 1 has the hard coat layer 12 which serves as an insulation layer. Moreover, even when the pressure sensitive adhesive sheet for batteries 1 according to the present embodiment is exposed to high temperatures and carbonization and the like occur in matrices (organic components) of the base material 11 and/or the hard coat layer 12, the metal oxide particles having insulation properties remain as an insulating film to ensure the insulation properties of the pressure sensitive adhesive sheet for batteries 1 itself. Other advantages are as follows. If a high voltage is partially applied to the pressure sensitive adhesive sheet for batteries 1 to flow a current through the pressure sensitive adhesive sheet for batteries 1 in its thickness direction, paths for the current in the base material 11 may alter into conductor paths. In such a case, even when carbonization and the like of matrices of the hard coat layer 12 occur along such paths for the current, the metal oxide particles having insulation properties exist in such paths to ensure the insulation properties of the pressure sensitive adhesive sheet for batteries 1 itself. Furthermore, formation of alternative paths for the conductor paths due to insulation breakdown will be more difficult because the hard coat layer 12, or an insulating film, exists at a location nearer to an adherend to which the pressure sensitive adhesive sheet for batteries 1 is attached.

In some cases, hydrofluoric acid may be generated when water reacts with a salt, such as lithium hexafluorophosphate, which is an electrolyte in an electrolyte solution. The metal oxide particles contained in the hard coat layer 12 of the pressure sensitive adhesive sheet for batteries 1 according to the present embodiment have low decomposability and solubility to the hydrofluoric acid and are therefore less likely to escape from the hard coat layer 12 even when the pressure sensitive adhesive sheet for batteries 1 is immersed in the electrolyte solution of a battery for a long time. Thus, the pressure sensitive adhesive sheet for batteries 1 according to the present embodiment is excellent in the insulation properties even when immersed in an electrolyte solution for a long time and then heated to high temperatures.

That is, owing to the existence of the above hard coat layer 12, the pressure sensitive adhesive sheet for batteries 1 according to the present embodiment is excellent in the insulation properties in an ordinary time, in a case of being heated to high temperatures, and further in a case of being immersed in an electrolyte solution for a long time and then heated to high temperatures.

In a battery in which the pressure sensitive adhesive sheet for batteries 1 according to the present embodiment having the actions and effects as the above, it is possible to suppress the performance deterioration due to the pressure sensitive adhesive sheet and suppress the erroneous operation, thermal runaway, and short circuit of the battery. The safety of the battery can thus be high.

1. Constitutional Elements 1-1. Base Material

In the pressure sensitive adhesive sheet for batteries 1 according to the present embodiment, the base material 11 may preferably have a high minimum voltage at which insulation breakdown occurs. For example, the minimum voltage may be preferably 1 kV or higher, particularly preferably 2 kV or higher, and further preferably 5 kV or higher. When the minimum voltage is 1 kV or higher, insulation breakdown of the base material 11 is less likely to occur and the reliability of the pressure sensitive adhesive sheet for batteries 1 can be higher.

The base material 11 may preferably have flame retardancy that satisfies the flame retardancy level V-0 according to the UL 94 standard. Owing to such flame retardancy of the base material 11, denaturation and deformation of the base material 11 can be suppressed even when the battery generates heat due to its ordinary use. Moreover, even if troubles occur in the battery and it generates excessive heat, ignition and/or burning of the base material 11 can be suppressed to prevent a serious accident.

The material of the substrate 11 can be appropriately selected from the viewpoints of insulation properties, flame retardancy, heat resistance, reactivity with an electrolyte solution, permeability to an electrolyte solution, and the like. In particular, it may be preferred to use a resin film as the base material 11. Examples of the resin film include films of polyesters such as polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate, polyolefin films such as a polyethylene film and polypropylene film, films of polymer that contains nitrogen in its main chain, such as a polyamide film, polyimide film and polyamideimide film, cellophane, a diacetyl cellulose film, triacetyl cellulose film, acetyl cellulose butyrate film, polyvinyl chloride film, polyvinylidene chloride film, polyvinyl alcohol film, ethylene-vinyl acetate copolymer film, polystyrene film, polycarbonate film, polymethylpentene film, polysulfone film, polyether ether ketone film, polyether sulfone film, polyether imide film, fluorine resin film, acrylic resin film, polyurethane resin film, norbornene-based polymer film, cyclic olefin-based polymer film, cyclic conjugated diene-based polymer film, vinyl alicyclic hydrocarbon polymer film, other resin films, and laminated films thereof. In particular, from the viewpoints of insulation properties and flame retardancy, films of a polymer that contains nitrogen in its main chain (the film may contain other components than the polymer, here and hereinafter) may be preferred, films of a polymer that has a nitrogen-containing ring structure in the main chain may be particularly preferred, and films of a polymer that has a nitrogen-containing ring structure and an aromatic ring structure in the main chain may be further preferred. Specifically, for example, a polyimide film, polyetherimide film, or polyether ether ketone film may be preferred, among which the polyimide film may be preferred because it is particularly excellent in the insulation properties and flame retardancy.

The thickness of the base material 11 may be preferably 5 to 200 μm, particularly preferably 10 to 100 μm, and further preferably 15 to 40 μm. When the thickness of the base material 11 is 5 μm or more, the base material 11 can have moderate rigidity and the occurrence of curl can be effectively suppressed even if curing shrinkage occurs during the formation of the hard coat layer 12 on the base material 11. On the other hand, the thickness of the base material 11 being 200 μm or less allows the pressure sensitive adhesive sheet for batteries 1 to have moderate flexibility and, even when the pressure sensitive adhesive sheet for batteries 1 is attached to a surface having a height difference, such as when an electrode and an electrode lead-out tab are fixed to each other, the pressure sensitive adhesive sheet for batteries 1 can well follow the height difference.

1-2. Hard Coat Layer (1) Composition of Hard Coat Layer

The hard coat layer 12 of the pressure sensitive adhesive sheet for batteries 1 according to the present embodiment is formed of a composition for hard coat layer that contains a metal oxide sol. The metal oxide sol is a sol of a metal oxide that has insulation properties. In other words, the hard coat layer 12 of the pressure sensitive adhesive sheet for batteries 1 according to the present embodiment contains metal oxide particles that are originated from the metal oxide sol and have insulation properties. As previously described, the pressure sensitive adhesive sheet for batteries 1 having such a hard coat layer 12 is excellent in the insulation properties in an ordinary time, in a case of being heated to high temperatures, and further in a case of being immersed in an electrolyte solution for a long time and then heated to high temperatures.

The hard coat layer 12 may preferably be a layer that is cured by irradiation with active energy rays. Accordingly, the composition for hard coat layer for forming the hard coat layer 12 may preferably contain an active energy ray-curable component and the above metal oxide sol.

(1-1) Active Energy Ray-Curable Component

The active energy ray-curable component is not particularly limited, provided that it can be cured by irradiation with active energy rays to exhibit desired hardness.

Specific examples of the active energy ray-curable component include various components, such as a polyfunctional (meth)acrylate-based monomer and (meth)acrylate-based prepolymer, among which the polyfunctional (meth)acrylate-based monomer and/or (meth)acrylate-based prepolymer may be preferred. The polyfunctional (meth)acrylate-based monomer and the (meth)acrylate-based prepolymer may each be used alone and both may also be used in combination. As used in the present description, the (meth)acrylate refers to both an acrylate and a methacrylate. The same applies to other similar terms.

Examples of the polyfunctional (meth)acrylate-based monomer include 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, caprolactone-modified dicyclopentenyl di(meth)acrylate, ethylene oxide-modified phosphoric acid di(meth)acrylate, allylated cyclohexyl di(meth)acrylate, isocyanurate di(meth)acrylate, trimethylol propane tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, propionic acid-modified dipentaerythritol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, tris(acryloxyethyl)isocyanurate, propionic acid-modified dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, caprolactone-modified dipentaerythritol hexa(meth)acrylate, and other appropriate polyfunctional (meth)acrylates. These may each be used alone and two or more types may also be used in combination. The polyfunctional (meth)acrylate-based monomer is not particularly restricted, but its molecular weight may more preferably be less than 1,000 from the viewpoint of preventing escape of the meal oxide particles from the hard coat layer 12 under the immersion in an electrolyte solution.

On the other hand, examples of the (meth)acrylate-based prepolymer include polyester acrylate-based, epoxy acrylate-based, urethane acrylate-based, and polyol acrylate-based prepolymers. One type of prepolymer may be used alone and two or more types may also be used in combination.

The glass-transition point after curing of the active energy ray-curable component which constitutes the hard coat layer 12 of the present embodiment may be preferably 130° C. or higher and more preferably 150° C. or higher, and an active energy ray-curable component of which the glass-transition point is not observed may be particularly preferred. When the glass-transition point of the active energy ray-curable component satisfies the above, the hard coat layer 12 can have excellent heat resistance, and a battery that includes the pressure sensitive adhesive sheet for batteries 1 provided with such a hard coat layer 12 can have excellent performance and safety.

When two or more types of the active energy ray-curable components are used in the hard coat layer 12 of the present embodiment, it may be preferred for them to have excellent compatibility with each other.

(1-2) Metal Oxide Sol

The metal oxide sol used in the present embodiment is a sol of a metal oxide that has insulating properties. Metal oxide particles in the metal oxide sol are less likely to escape from the hard coat layer 12 even when immersed in an electrolyte solution for a long time as compared with non-metal oxide particles in a non-metal oxide sol such as silica sol, and can maintain the insulation properties possessed by the metal oxide particles when heated to high temperatures.

Examples of a such metal oxide sol include alumina sol, zirconia sol, magnesia sol, titania sol, barium titanate sol, hafnia sol, yttria sol, germania sol, zinc oxide sol, copper oxide sol, tungsten oxide sol, cobalt oxide sol, and tin oxide sol. Among these, alumina sol, zirconia sol, and magnesia sol may be preferred because they are excellent in the insulation properties and the metal oxide particles are less likely to escape from the hard coat layer 12 even when immersed in an electrolyte solution for a long, and alumina sol and zirconia sol may be further preferable. These may each be used alone and two or more types may also be used in combination.

From the viewpoint of compatibility with the active energy ray-curable component, the dispersion medium of the metal oxide sol may preferably be propylene glycol monomethyl ether, methyl isobutyl ketone, ethyl acetate, and/or toluene. The concentration of the metal oxide particles in the metal oxide sol may be preferably 10 to 50 mass %, particularly preferably 12 to 40 mass %, and further preferably 15 to 30 mass %.

The average particle diameter of the metal oxide particles contained in the metal oxide sol may be preferably 1 to 1,000 nm, particularly preferably 5 to 500 nm, and further preferably 10 to 200 nm. When the average particle diameter of the metal oxide particles is 1 nm or more, the hard coat layer 12 can have rigidity and it is thus possible to prevent breakage, such as tear and puncture, of the pressure sensitive adhesive sheet for batteries 1 due to impact and the like under high temperatures or immersion in an electrolyte solution. When the average particle diameter of the metal oxide particles is 1,000 nm or less, the dispersibility of the metal oxide particles in the composition for hard coat layer can be excellent and it is thus possible to effectively prevent the occurrence of irregularities on the surface of the hard coat layer 12 opposite to the base material 11 during the formation of the hard coat layer 12 on the base material 11. Moreover, when the pressure sensitive adhesive layer 13 is formed on that surface, significantly high smoothness can be obtained on the surface of the pressure sensitive adhesive layer 13 opposite to the hard coat layer 12. This allows the pressure sensitive adhesive layer 13 to exhibit an excellent adhesion property to an adherend. The average particle diameter of the metal oxide particles is to be measured using a laser diffraction scattering-type particle diameter distribution measuring apparatus.

The content of the metal oxide sol in the composition for hard coat layer may be preferably 1 volume part or more, particularly preferably 5 volume parts or more, and further preferably 10 volume parts or more to 100 volume parts of the active energy ray-curable component. From another aspect, the content may be preferably 500 volume parts or less, particularly preferably 200 volume parts or less, and further preferably 100 volume parts or less. When the content of the metal oxide sol in the composition for hard coat layer falls within the above range, the hard coat layer 12 can have more excellent insulation properties, in particular insulation properties when heated to high temperatures after immersion in an electrolyte solution for long time, while maintaining the strength of the hard coat layer 12.

The content of the metal oxide particles in the hard coat layer 12 may be preferably 0.01 cm³/m² or more, particularly preferably 0.1 cm³/m² or more, and further preferably 0.2 cm³/m² or more. From another aspect, the content may be preferably 7 cm³/m² or less, particularly preferably 5 cm³/m² or less, and further preferably 3 cm³/m² or less. When the content of the metal oxide particles in the hard coat layer 12 falls within the above range, the hard coat layer 12 can have excellent insulation properties, in particular insulation properties when heated to high temperatures after immersion in an electrolyte solution for long time, while maintaining the strength of the hard coat layer 12.

(1-3) Other Components

The composition for forming the hard coat layer 12 of the present embodiment may contain various additives in addition to the above-described components. Examples of such additives include a photopolymerization initiator, antioxidant, antistatic, silane coupling agent, antiaging agent, thermal polymerization inhibitor, colorant, surfactant, storage stabilizer, plasticizer, glidant, antifoam, and organic-based filler.

When the hard coat layer 12 is formed using ultraviolet rays as the active energy rays, it is preferred to use a photopolymerization initiator. The photopolymerization initiator is not particularly limited, provided that it functions as a photopolymerization initiator for the active energy ray-curable component to be used. Examples of the photopolymerization initiator include acylphosphine oxide compounds, benzoin compounds, acetophenone compounds, titanocene compounds, thioxanthone compounds, and peroxide compounds. Specific examples include 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propane-1-one, 2,2-dimethoxy-1,2-diphenylethan-1-one, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzyl diphenyl sulfide, tetramethyl thiuram monosulfide, azobisisobutyronitrile, dibenzyl, diacetyl, and β-chloroanthraquinone. These may each be used alone and two or more types may also be used in combination.

The content of the above photopolymerization initiator in the composition for hard coat layer may be preferably 0.1 to 20 mass parts in general and particularly preferably 1 to 15 mass parts to 100 mass parts of the active energy ray-curable component.

(2) Thickness of Hard Coat Layer

The thickness of the hard coat layer 12 may be preferably 0.1 to 10 μm, particularly preferably 0.5 to 7 μm, and further preferably 1 to 4 μm. When the thickness of the hard coat layer 12 is 0.1 μm or more, permeation of the electrolyte solution through the hard coat layer 12 can be effectively blocked and the previously-described insulation properties can be more excellent. On the other hand, the thickness of the hard coat layer 12 being 10 μm or less allows the pressure sensitive adhesive sheet for batteries 1 to have moderate flexibility and, even when the pressure sensitive adhesive sheet for batteries 1 is attached to a surface having a height difference, such as when an electrode and an electrode lead-out tab are fixed to each other, the pressure sensitive adhesive sheet for batteries 1 can well follow the height difference.

(3) Physical Properties of Hard Coat Layer

In the pressure sensitive adhesive sheet for batteries 1 according to the present embodiment, the hard coat layer 12 in a state of being provided on the base material 11 may preferably has a property that, when the hard coat layer 12 is rubbed at a load of 250 g/cm² using #0000 steel wool to reciprocate it ten times within a length of 10 cm, no scratches occur. When the hard coat layer 12 is evaluated to have such steel wool resistance, permeation of the electrolyte solution through the hard coat layer 12 can be effectively blocked, and the escape of the metal oxide particles due to swelling of the hard coat layer 12 can be effectively suppressed.

1-3. Pressure Sensitive Adhesive Layer

A pressure sensitive adhesive that constitutes the pressure sensitive adhesive layer 13 is not particularly limited and can be appropriately selected from the viewpoints of solubility in an electrolyte solution, flame retardancy, heat resistance, insulating properties, and the like. In particular, an acrylic-based pressure sensitive adhesive, silicone-based pressure sensitive adhesive, rubber-based pressure sensitive adhesive, and urethane-based pressure sensitive adhesive may be preferred as the pressure sensitive adhesive which constitutes the pressure sensitive adhesive layer 13. Among these, an acrylic-based pressure sensitive adhesive may be particularly preferred from the viewpoints of an adhesion property to the hard coat layer 12, an electrode and the like, easy delicate adjustment of the adhesive strength, etc.

The acrylic-based pressure sensitive adhesive may preferably be obtained from a pressure sensitive adhesive composition that contains a (meth)acrylic ester polymer (A) (this composition may be referred to as a “pressure sensitive adhesive composition P,” hereinafter). The pressure sensitive adhesive composition P may preferably contain a crosslinker (B) in addition to the (meth)acrylic ester polymer (A) and particularly preferably further contain a silane coupling agent (C). As used in the present description, the term “polymer” encompasses the concept of a “copolymer.”

(1) Components (1-1) (Meth)Acrylic Ester Polymer (A)

The (meth)acrylic ester polymer (A) may contain (meth)acrylic alkyl ester of which the carbon number of alkyl group is 1 to 20, as the monomer unit which constitutes the polymer, thereby to exhibit a preferred pressure sensitive adhesive property. Examples of the (meth)acrylic alkyl ester of which the carbon number of alkyl group is 1 to 20 include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate. Among these, (meth)acrylic alkyl ester of which the carbon number of alkyl group is 1 to 8 may preferably be contained from the viewpoint of further improving the pressure sensitive adhesive property. These may each be used alone and two or more types may also be used in combination.

The (meth)acrylic ester polymer (A) may preferably contain 50 mass % or more, particularly preferably contain 60 mass % or more, and further preferably contain 70 mass % or more of the (meth)acrylic alkyl ester of which the carbon number of alkyl group is 1 to 20, as the monomer unit which constitutes the polymer. When containing 50 mass % or more of the above (meth)acrylic alkyl ester, the (meth)acrylic ester polymer (A) can exhibit an appropriate pressure sensitive adhesive property. From another aspect, the (meth)acrylic ester polymer (A) may preferably contain 99 mass % or less, particularly preferably contain 97 mass % or less, and further preferably contain 90 mass % or less of the (meth)acrylic alkyl ester of which the carbon number of alkyl group is 1 to 20, as the monomer unit which constitutes the polymer. When the content of the above (meth)acrylic alkyl ester is 99 mass % or less, an appropriate amount of other monomer components can be introduced into the (meth)acrylic ester polymer (A).

In the (meth)acrylic ester polymer (A), it may also be preferred to use a combination of a monomer (hard monomer) having a glass-transition temperature (Tg) of higher than 0° C. as that of a homopolymer and a monomer (soft monomer) having a glass-transition temperature (Tg) of 0° C. or lower as that of a homopolymer, as the (meth)acrylic alkyl ester of which the carbon number of alkyl group is 1 to 20, that is, as the monomer unit which constitutes the polymer. This can further improve the resistance to dissolution into an electrolyte solution. In this case, the mass ratio of the hard monomer and the soft monomer may be preferably 5:95 to 40:60 and particularly preferably 20:80 to 30:70.

Examples of the above hard monomer include methyl acrylate (Tg 10° C.), methyl methacrylate (Tg 105° C.), isobornyl acrylate (Tg 94° C.), isobornyl methacrylate (Tg 180° C.), adamantyl acrylate (Tg 115° C.), and adamantyl methacrylate (Tg 141° C.). These may each be used alone and two or more types may also be used in combination.

Among the above hard monomers, the methyl acrylate, methyl methacrylate, and isobornyl acrylate may be preferred and the methyl acrylate and methyl methacrylate may be particularly preferred from the viewpoint of exhibiting high performance of the hard monomer while preventing negative effects on the properties such as a pressure sensitive adhesive property.

Preferred examples of the above soft monomer include an acrylic alkyl ester that has a linear chain or branched chain alkyl group of which the carbon number is 2 to 12. For example, 2-ethylhexyl acrylate (Tg −70° C.), n-butyl acrylate (Tg −54° C.) and the like may be preferred and n-butyl acrylate may be particularly preferred. These may each be used alone and two or more types may also be used in combination.

If desired, the (meth)acrylic ester polymer (A) may contain other monomers as the monomer unit which constitutes the polymer. Examples of the other monomers include a monomer that contains a reactive functional group and a monomer that does not contain a reactive functional group.

Examples of the monomer which contains a reactive functional group (reactive functional group-containing monomer) include a monomer having a carboxy group in the molecule (carboxy group-containing monomer), a monomer having a hydroxyl group in the molecule (hydroxyl group-containing monomer), and a monomer having an amino group in the molecule (amino group-containing monomer). The (meth)acrylic ester polymer (A) may preferably contain the carboxy group-containing monomer, among the above, as the monomer unit which constitutes the polymer. When a metal chelate-based crosslinker is used as the crosslinker (B), which will be described later, carboxy groups originated from the carboxy group-containing monomer react with the metal chelate-based crosslinker when the (meth)acrylic ester polymer (A) is crosslinked, thereby to form a crosslinked structure that is a three-dimensional network structure. The pressure sensitive adhesive having the crosslinked structure due to the reaction between the carboxy groups and the metal chelate-based crosslinker is highly resistant to an electrolyte solution, in particular to a nonaqueous electrolyte solution, and is less likely to dissolve into the electrolyte solution even in contact therewith.

Examples of the carboxy group-containing monomer include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Among these, acrylic acid may be preferred. According to the acrylic acid, the above effects may be more excellent. The above carboxy group-containing monomer may be used alone and two or more types may also be used in combination.

The (meth)acrylic ester polymer (A) may preferably contain 0.5 mass % or more, particularly preferably contain 1 mass % or more, and further preferably contain 3 mass % or more as the lower limit of the carboxy group-containing monomer, as the monomer unit which constitutes the polymer. From another aspect, the (meth)acrylic ester polymer (A) may preferably contain 30 mass % or less, particularly preferably contain 25 mass % or less, and further preferably contain 20 mass % or less as the upper limit of the carboxy group-containing monomer, as the monomer unit which constitutes the polymer. When the (meth)acrylic ester polymer (A) contains the above amount of the carboxy group-containing monomer as the monomer unit, the above effects may be more excellent in the obtained pressure sensitive adhesive.

Examples of the hydroxyl group-containing monomer include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. These may each be used alone and two or more types may also be used in combination.

Examples of the amino group-containing monomer include aminoethyl (meth)acrylate and n-butylaminoethyl (meth)acrylate. These may each be used alone and two or more types may also be used in combination.

In order not to inhibit the effects obtained by the crosslinked structure due to the reaction between the carboxy groups and the metal chelate-based crosslinker, it may be preferred to use only the previously-described carboxy group-containing monomer as a reactive functional group-containing monomer.

Examples of the monomer which does not contain a reactive functional group include alkoxyalkyl (meth)acrylates such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, (meth)acrylic esters having a non-crosslinkable tertiary amino group, such as N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate and (meth)acryloyl morpholine, (meth)acrylamide, dimethyl acrylamide, vinyl acetate, and styrene. These may each be used alone and two or more types may also be used in combination.

The polymerization form of the (meth)acrylic ester polymer (A) may be a random copolymer and may also be a block copolymer.

The weight-average molecular weight of the (meth)acrylic ester polymer (A) may be preferably 50,000 or more, more preferably 100,000 or more, particularly preferably 200,000 or more, and further preferably 500,000 or more as the lower limit. When the lower limit of the weight-average molecular weight of the (meth)acrylic ester polymer (A) satisfies the above, the obtained pressure sensitive adhesive can have more excellent resistance to dissolution into an electrolyte solution.

From another aspect, the weight-average molecular weight of the (meth)acrylic ester polymer (A) may be preferably 2,500,000 or less, more preferably 2,000,000 or less, particularly preferably 1,500,000 or less, and further preferably 1,200,000 or less as the upper limit. When the upper limit of the weight-average molecular weight of the (meth)acrylic ester polymer (A) satisfies the above, the obtained pressure sensitive adhesive can have more excellent adhesive strength. As used in the present description, the weight-average molecular weight refers to a standard polystyrene equivalent value that is measured using a gel permeation chromatography (GPC) method.

In the pressure sensitive adhesive composition P, one type of the (meth)acrylic ester polymer (A) may be used alone and two or more types may also be used in combination.

(1-2) Crosslinker (B)

It suffices that the crosslinker (B) is reactive with a reactive functional group of the (meth)acrylic ester polymer (A). Examples of the crosslinker (B) include an isocyanate-based crosslinker, epoxy-based crosslinker, amine-based crosslinker, melamine-based crosslinker, aziridine-based crosslinker, hydrazine-based crosslinker, aldehyde-based crosslinker, oxazoline-based crosslinker, metal alkoxide-based crosslinker, metal chelate-based crosslinker, metal salt-based crosslinker, and ammonium salt-based crosslinker. One type of the crosslinker (B) may be used alone and two or more types may also be used in combination.

Among the above, the metal chelate-based crosslinker may preferably be used as the crosslinker (B). In this case, the (meth)acrylic ester polymer (A) may preferably contain a carboxy group-containing monomer as the monomer unit which constitutes the polymer. As previously described, according to this combination, the obtained pressure sensitive adhesive is highly resistant to an electrolyte solution, in particular to a nonaqueous electrolyte solution, and is less likely to dissolve into the electrolyte solution even in contact therewith. Thus, the pressure sensitive adhesive does not negatively affect the battery performance and it is possible to suppress the erroneous operation and the like of the battery due to dissolution of the pressure sensitive adhesive.

Examples of a compound that can be used as the metal chelate-based crosslinker include metal chelate compounds in which the metal atom is aluminum, zirconium, titanium, zinc, iron, tin, or other appropriate metal. Among these, an aluminum chelate compound may be particularly preferred. The aluminum chelate compound particularly effectively exhibits the previously-described resistance to dissolution into an electrolyte solution.

Examples of the aluminum chelate compound include diisopropoxyaluminum monooleylacetoacetate, monoisopropoxyaluminum bisoleylacetoacetate, monoisopropoxyaluminum monooleate monoethylacetoacetate, diisopropoxyaluminum monolaurylacetoacetate, diisopropoxyaluminum monostearylacetoacetate, diisopropoxyaluminum monoisostearylacetoacetate, monoisopropoxyaluminum mono-N-lauroyl-β-alanate monolaurylacetoacetate, aluminum tris(acetylacetonate), monoacetylacetonate aluminum bis(isobutylacetoacetate) chelate, monoacetylacetonate aluminum bis (2-ethylhexylacetoacetate) chelate, monoacetylacetonate aluminum bis(dodecylacetoacetate) chelate, and monoacetylacetonate aluminum bis(oleylacetoacetate) chelate. Among these, the aluminum tris(acetylacetonate) may be preferred from the viewpoint of the above effects. These may each be used alone and two or more types may also be used in combination.

Examples of other metal chelate compounds include titanium tetrapropionate, titanium tetra-n-butyrate, titanium tetra-2-ethylhexanoate, zirconium sec-butyrate, zirconium diethoxy-tert-butyrate, triethanolamine titanium dipropionate, ammonium salt of titanium lactate, and tetraoctyleneglycol titanate. These may each be used alone and two or more types may also be used in combination.

One type of the above metal chelate-based crosslinker may be used alone and two or more types may also be used in combination.

The content of the metal chelate-based crosslinker in the pressure sensitive adhesive composition P according to the present embodiment may be preferably 0.1 mass parts or more, more preferably 0.2 mass parts or more, particularly preferably 0.3 mass parts or more, and further preferably 0.5 mass parts or more as the lower limit to 100 mass parts of the (meth)acrylic ester polymer (A). From another aspect, the content of the metal chelate-based crosslinker may be preferably 5 mass parts or less, particularly preferably 4 mass parts or less, and further preferably 3 mass parts or less as the upper limit. When the content of the metal chelate-based crosslinker falls within the above range, the previously-described effects can be more excellent.

The pressure sensitive adhesive composition P according to the present embodiment may contain other crosslinkers than the metal chelate-based crosslinker. Examples of other crosslinkers than the metal chelate-based crosslinker include an isocyanate-based crosslinker, epoxy-based crosslinker, amine-based crosslinker, melamine-based crosslinker, aziridine-based crosslinker, hydrazine-based crosslinker, aldehyde-based crosslinker, oxazoline-based crosslinker, metal alkoxide-based crosslinker, metal salt-based crosslinker, and ammonium salt-based crosslinker. Among the above, the isocyanate-based crosslinker may be preferred because it does not inhibit the reaction between the carboxyl groups of the (meth)acrylic ester polymer (A) and the metal chelate-based crosslinker and reacts with the carboxyl groups.

The isocyanate-based crosslinker contains at least a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate, biuret bodies and isocyanurate bodies thereof, and adduct bodies that are reaction products with low molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylol propane, and castor oil. Among these, trimethylolpropane-modified aromatic polyisocyanate may be preferred, trimethylolpropane-modified tolylene diisocyanate and trimethylolpropane-modified xylylene diisocyanate may be particularly preferred, and trimethylolpropane-modified tolylene diisocyanate may be further preferred from the viewpoint of reactivity with hydroxyl groups. These may each be used alone and two or more types may also be used in combination.

When the isocyanate-based crosslinker is used in combination with the metal chelate-based crosslinker, the mass ratio of the metal chelate-based crosslinker and the isocyanate-based crosslinker may be preferably 99:1 to 1:99, particularly preferably 90:10 to 5:95, and further preferably 20:80 to 10:90.

(1-3) Silane Coupling Agent (C)

The pressure sensitive adhesive composition P may preferably contain a silane coupling agent (C). When the silane coupling agent (C) is contained, excellent adhesive strength is exhibited to an adherend (in particular, to a metal member) even in a case in which the pressure sensitive layer 13 is in contact with an electrolyte solution. This can further suppress the delamination of the pressure sensitive adhesive sheet for batteries 1 from an adherend and can also suppress the deterioration of the battery performance due to the pressure sensitive adhesive sheet for batteries 1. Moreover, the obtained pressure sensitive adhesive layer 13 can have a higher adhesion property to the hard coat layer 12. When the pressure sensitive adhesive sheet for batteries 1 is immersed in an electrolyte solvent, therefore, delamination and the like can be prevented from occurring at the interface between the hard coat layer 12 and the pressure sensitive adhesive layer 13, and the adhesive strength after the immersion in the electrolyte solvent can be high. Furthermore, when the release sheet 14 is removed from the pressure sensitive adhesive layer 13, it is possible to effectively suppress delamination of the pressure sensitive adhesive layer 13 from the hard coat layer 12 due to transfer of the pressure sensitive adhesive layer 13 to the release sheet 14.

Preferred examples of the silane coupling agent (C) include an organosilicon compound that has at least one alkoxysilyl group in the molecule and is well compatible with the (meth)acrylic ester polymer (A).

Examples of such a silane coupling agent (C) include polymerizable unsaturated group-containing silicon compounds such as vinyltrimethoxysilane, vinyltriethoxysilane and methacryloxypropyltrimethoxysilane, silicon compounds having an epoxy structure, such as 3-glycidoxypropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, mercapto group-containing silicon compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane and 3-mercaptopropyldimethoxymethylsilane, amino group-containing silicon compounds such as 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-chloropropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, and condensates of at least one of these and an alkyl group-containing silicon compound such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane and ethyltrimethoxysilane. Among these, the silicon compound having an epoxy structure may be preferred and the 3-glycidoxypropyltrimethoxysilane may be particularly preferred from the viewpoint of the above effects. These may each be used alone and two or more types may also be used in combination.

The content of the silane coupling agent (C) in the pressure sensitive adhesive composition P may be preferably 0.01 mass parts or more, more preferably 0.05 mass parts or more, particularly preferably 0.1 mass parts or more, and further preferably 0.4 mass parts or more to 100 mass parts of the (meth)acrylic ester polymer (A). From another aspect, the content may be preferably 5 mass parts or less, more preferably 4 mass parts or less, particularly preferably 3 mass parts or less, and further preferably 1.5 mass parts or less. When the content of the silane coupling agent (C) falls within the above range, the adhesive strength after immersion in an electrolyte solvent can be more excellent.

(1-4) Additives

If desired, the pressure sensitive adhesive composition P may contain various additives, such as a tackifier, antioxidant, softening agent, and filler, which are commonly used in an acrylic-based pressure sensitive adhesive. The additives which constitute the pressure sensitive adhesive composition P are deemed not to include a polymerization solvent and a diluent solvent, which will be described later.

(2) Production of Pressure Sensitive Adhesive Composition

The pressure sensitive adhesive composition P can be produced through producing the (meth)acrylic ester polymer (A) and, if necessary, adding the crosslinker (B), the silane coupling agent (C), additives, and the like to the obtained (meth)acrylic ester polymer (A).

The (meth)acrylic ester polymer (A) can be produced by polymerizing a mixture of the monomers which constitute the polymer using a commonly-used radical polymerization method. Polymerization of the (meth)acrylic ester polymer (A) can be carried out, such as by a solution polymerization method using a polymerization initiator, if desired. Examples of the polymerization solvent include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, and methyl ethyl ketone and two or more types thereof may also be used in combination.

Examples of the polymerization initiator include azo-based compounds and organic peroxides and two or more types thereof may also be used in combination. Examples of the azo-based compounds include 2,2′-azobisisobutyronitrile, 2,2′-azobis(2-methylbutyronitrile), 1,1′-azobis(cyclohexane 1-carbonitrile), 2,2′-azobis(2,4-dimethylvaleronitrile), 2,2′-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2′-azobis(2-methylpropionate), 4,4′-azobis(4-cyanovaleric acid), 2,2′-azobis(2-hydroxymethylpropionitrile), and 2,2′-azobis[2-(2-imidazolin-2-yl)propane].

Examples of the organic peroxide include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(2-ethoxyethyl)peroxydicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxybivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, and diacetyl peroxide.

The weight-average molecular weight of the polymer to be obtained can be adjusted by compounding a chain transfer agent, such as 2-mercaptoethanol, in the above polymerization step.

After the (meth)acrylic ester polymer (A) is obtained, the pressure sensitive adhesive composition P may be obtained through adding, if desired, the crosslinker (B), the silane coupling agent (C), additives and the like to the solution of the (meth)acrylic ester polymer (A) and sufficiently mixing them.

For adjustment of a suitable viscosity for coating and/or adjustment of a desired film thickness of the pressure sensitive adhesive layer, the pressure sensitive adhesive composition P may be appropriately diluted with a diluent solvent or the like in addition to the previously-described polymerization solvent to obtain a coating liquid, which will be described later. Examples of the diluent solvent include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, and methyl ethyl ketone and two or more types thereof may also be used in combination.

(3) Physical Properties of Pressure Sensitive Adhesive/Pressure Sensitive Adhesive Layer

In the pressure sensitive adhesive sheet for batteries 1 according to the present embodiment, after the pressure sensitive adhesive which constitutes the pressure sensitive adhesive layer 13 is immersed in a solvent of a nonaqueous electrolyte solution at 80° C. for 72 hours, the gel fraction of the pressure sensitive adhesive may be preferably 50% or more, particularly preferably 60% or more, and further preferably 70% or more as the lower limit. The lower limit of the above gel fraction satisfying the above can suppress the amount of dissolution of the pressure sensitive adhesive when the pressure sensitive adhesive layer 13 is in contact with an electrolyte solution. This can more effectively suppress the erroneous operation and the like of the battery due to dissolution of the pressure sensitive adhesive.

From another aspect, the upper limit of the above gel fraction may be preferably 100% or less, particularly preferably 99% or less, and further preferably 98% or less. The upper limit of the gel fraction being 98% or less allows the pressure sensitive adhesive sheet for batteries 1 to have moderate flexibility and, even when the pressure sensitive adhesive sheet for batteries 1 is attached to a surface having a height difference, such as when an electrode and an electrode lead-out tab are fixed to each other, the pressure sensitive adhesive sheet for batteries 1 can well follow the height difference.

The solvent of a nonaqueous electrolyte solution as used herein may be a prepared liquid obtained by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 1:1. A method of testing the gel fraction is as described in the exemplary test, which will be described later.

(4) Thickness of Pressure Sensitive Adhesive Layer

The thickness (a value measured in accordance with JIS K7130) of the pressure sensitive adhesive layer 13 may be preferably 1 to 50 μm, particularly preferably 3 to 15 μm, and further preferably 4 to 9 μm. When the thickness of the pressure sensitive adhesive layer 13 is 1 μm or more, the pressure sensitive adhesive sheet for batteries 1 can exhibit good adhesive strength. When the thickness of the pressure sensitive adhesive layer 13 is 50 μm or less, the amount of electrolyte solution infiltrating into the pressure sensitive adhesive layer 13 from its end parts can be effectively reduced.

1-4. Release Sheet

The release sheet 14 is to protect the pressure sensitive adhesive layer until the use of the pressure sensitive adhesive sheet for batteries 1 and is removed when using the pressure sensitive adhesive sheet for batteries 1. In the pressure sensitive adhesive sheet for batteries 1 according to the present embodiment, the release sheet 14 may not necessarily be required.

Examples of the release sheet 14 to be used include a polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polyurethane film, ethylene-vinyl acetate film, ionomer resin film, ethylene-(meth)acrylic acid copolymer film, ethylene-(meth)acrylic ester copolymer film, polystyrene film, polycarbonate film, polyimide film, fluorine resin film, and liquid crystal polymer film. Crosslinked films thereof may also be used. A laminate film obtained by laminating a plurality of such films may also be used.

It may be preferred to perform release treatment for the release surface (surface to be in contact with the pressure sensitive adhesive layer 13) of the release sheet 14. Examples of a release agent to be used for the release treatment include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents.

The thickness of the release sheet 14 is not particularly restricted, but may ordinarily be about 20 to 150 μm.

2. Physical Properties Etc. of Pressure Sensitive Adhesive Sheet for Batteries

The adhesive strength (adhesive strength before immersion in electrolyte solvent) of the pressure sensitive adhesive sheet for batteries 1 according to the present embodiment to an aluminum plate may be preferably 0.5 N/25 mm or more, particularly preferably 0.75 N/25 mm or more, and further preferably 1.0 N/25 mm or more as the lower limit. When the lower limit of the adhesive strength of the pressure sensitive adhesive sheet for batteries 1 before immersion in the electrolyte solvent satisfies the above, a trouble is less likely to occur that the pressure sensitive adhesive sheet for batteries 1 delaminates from an adherend (in particular, a metal member) before the pressure sensitive adhesive sheet for batteries 1 comes into contact with the electrolyte solution. The upper limit of the above adhesive strength before immersion in the electrolyte solvent is not particularly limited, but may be preferably 50 N/25 mm or less in general, particularly preferably 40 N/25 mm or less, and further preferably 30 N/25 mm or less. As used in the present description, the adhesive strength refers basically to a peel strength that is measured using a method of 180° peeling in accordance with JIS 20237: 2009. Details of the method of measurement are as described in the exemplary test, which will be described later.

In an ordinary time (under ordinary temperature, humidity, and pressure), the resistance value in the thickness direction of the pressure sensitive adhesive sheet for batteries 1 (excluding the release sheet 14) may preferably be 1.0×10¹⁰Ω or higher. When the resistance value in the thickness direction of the pressure sensitive adhesive sheet for batteries 1 is the above value or higher, the pressure sensitive adhesive sheet for batteries 1 can be said to be excellent in the insulation properties and it is thus possible to suppress the occurrence of short circuit and/or thermal runaway in the battery in which the pressure sensitive adhesive sheet for batteries 1 is used. The upper limit of the above resistance value is not particularly limited, but may preferably be 1.0×10¹⁶Ω or lower in general.

As used in the present description, the resistance value in the thickness direction of a pressure sensitive adhesive sheet for batteries may be measured through attaching the pressure sensitive adhesive sheet for batteries to an aluminum plate having a thickness of 1 mm to prepare a laminate and bringing terminals of a circuit tester into contact with the pressure sensitive adhesive sheet for batteries located at a surface of the laminate and the aluminum plate located at the other surface of the laminate. Details are as described in the test which will be described later.

After the pressure sensitive adhesive sheet for batteries 1 is heated in a nitrogen atmosphere at 800° C. for 1 hour, the resistance value in the thickness direction of the pressure sensitive adhesive sheet for batteries 1 (excluding the release sheet 14) may preferably be 1.0×10¹⁰Ω or higher. When the above resistance value is the above value or higher, the pressure sensitive adhesive sheet for batteries 1 can be said to be excellent in the insulation properties even when heated to high temperatures.

After the pressure sensitive adhesive sheet for batteries 1 is immersed in a nonaqueous electrolyte solution and heated at 80° C. for 4 weeks and subsequently heated in a nitrogen atmosphere at 800° C. for 1 hour, the resistance value in the thickness direction of the pressure sensitive adhesive sheet for batteries 1 (excluding the release sheet 14) may preferably be 1.0×10¹⁰Ω or higher. When the above resistance value is the above value or higher, the pressure sensitive adhesive sheet for batteries 1 can be said to be excellent in the insulation properties even when immersed in an electrolyte solution for a long time. The nonaqueous electrolyte solution as used herein is a prepared liquid that is obtained through mixing ethylene carbonate and diethyl carbonate at a volume ratio of 1:1 to make a mixture liquid and dissolving lithium hexafluorophosphate (LiPF₆) in the mixture liquid at a concentration of 1 mol/L.

The thickness of the pressure sensitive adhesive sheet for batteries 1 (excluding the thickness of the release sheet 14) may be preferably 10 to 250 μm, particularly preferably 15 to 110 μm, and further preferably 20 to 45 μm. When the thickness of the pressure sensitive adhesive sheet for batteries 1 falls within the above range, the pressure sensitive adhesive sheet for batteries 1 can be more suitable in which both the adhesive strength and the insulation properties are excellent.

3. Production Method for Pressure Sensitive Adhesive Sheet for Batteries

The pressure sensitive adhesive sheet for batteries 1 according to the present embodiment can be produced, for example, through preparing a laminate of the base material 11 and the hard coat layer 12, preparing a laminate of the pressure sensitive adhesive layer 13 and the release sheet 14, and attaching these laminates to each other so that the hard coat layer 12 and the pressure sensitive adhesive layer 13 come to contact with each other. From the viewpoint of enhancing the interfacial adhesion between the hard coat layer 12 and the pressure sensitive adhesive layer 13, it may be preferred to perform surface treatment such as corona treatment and plasma treatment for a surface to be attached of any one of these layers or surfaces to be attached of both of these layers and then attach these layers to each other.

The laminate of the base material 11 and the hard coat layer 12 can be prepared, for example, in the following manner. First, one main surface of the base material 11 may be coated with a coating liquid that contains the composition for hard coat layer and may further contain a solvent if desired, and the coating liquid may be dried. The method of coating with the coating liquid may be performed using an ordinary method, such as a bar coating method, knife coating method, Meyer bar method, roll coating method, blade coating method, die coating method, and gravure coating method. Drying can be performed, for example, by heating at 80° C. to 150° C. for about 30 seconds to 5 minutes.

Thereafter, the layer obtained by drying the above coating liquid may be irradiated with active energy rays to cure the layer to form the hard coat layer 12. As the active energy rays, for example, electromagnetic wave or charged particle radiation having an energy quantum can be used and, specifically, ultraviolet rays, electron rays or the like can be used. In particular, ultraviolet rays may be preferred because of easy management. Irradiation with ultraviolet rays can be performed using a high pressure mercury lamp, xenon lamp or the like, and the irradiance level of ultraviolet rays may be preferably about 50 to 1,000 mW/cm² as the illuminance. The light amount may be preferably 50 to 10,000 mJ/cm², more preferably 80 to 5,000 mJ/cm², and particularly preferably 200 to 2,000 mJ/cm². On the other hand, irradiation with electron rays can be performed using an electron ray accelerator or the like, and the irradiance level of electron rays may be preferably about 10 to 1,000 krad.

The laminate of the pressure sensitive adhesive layer 13 and the release sheet 14 can be prepared, for example, in the following manner.

The release surface of the release sheet 14 may be coated with a coating liquid that contains the previously-described pressure sensitive adhesive composition P and may further contain a solvent if desired, and heating treatment may be performed to form a coating film. The formed coating film itself may be the pressure sensitive adhesive layer 13 if an aging time is not necessary. If the aging time is necessary, the formed coating film may become the pressure sensitive adhesive layer 13 after the aging time passes.

Drying treatment when volatilizing a diluent solvent and the like of the coating liquid can also serve as the above heating treatment. When performing the heating treatment, the heating temperature may be preferably 50° C. to 150° C. and particularly preferably 70° C. to 120° C. The heating time may be preferably 30 seconds to 10 minutes and particularly preferably 50 seconds to 2 minutes. After the heating treatment, if necessary, an aging time at an ordinary temperature (e.g. 23° C., 50% RH) for about 1 to 2 weeks may be provided.

The pressure sensitive adhesive sheet for batteries 1 may be produced by laminating the above two laminates so that the pressure sensitive adhesive layer 13 and the hard coat layer 12 are in contact with each other. In an embodiment, the aging time for the pressure sensitive adhesive layer 13 may be provided after the lamination with the hard coat layer 12.

Another production method for the pressure sensitive adhesive sheet for batteries 1 according to the present embodiment may include forming the hard coat layer 12 and the pressure sensitive adhesive layer 13 in this order on the base material 11.

<Lithium-Ion Battery>

A lithium-ion battery according to an embodiment of the present invention may be configured such that two or more conductors are fixed in a state in which the two or more conductors are in contact with each other in the battery using the previously-described pressure sensitive adhesive sheet for batteries. It may be preferred that at least one of the two or more conductors be in a sheet-like shape while at least another one be in a line-like or a tape-like shape. A lithium-ion battery according to a preferred embodiment will be described below.

As illustrated in FIG. 2, the lithium-ion battery 2 according to the present embodiment may comprise a bottomed cylindrical exterior body 21 of which the bottom part constitutes a negative electrode terminal 23, a positive electrode terminal 22 provided at an opening part of the exterior body 21, and an electrode body 24 provided inside the exterior body 21. An electrolyte solution may be enclosed in the lithium-ion battery 2.

The electrode body 24 may comprise a positive electrode collector 241 laminated with a positive electrode active material layer 241 a, a negative electrode collector 242 laminated with a negative electrode active material layer 242 a, and a separator 243 interposed therebetween. Each of them is in a sheet-like (belt-like) shape. The laminate of the positive electrode collector 241 and the positive electrode active material layer 241 a may be referred to as a positive electrode while the laminate of the negative electrode collector 242 and the negative electrode active material layer 242 a may be referred to as a negative electrode, and the positive electrode and the negative electrode may be collectively referred to as an electrode or electrodes. The positive electrode, the negative electrode, and the separator 243 may be wound up together and then inserted inside the exterior body 21.

As illustrated in FIG. 3, a line-like or tape-like electrode lead-out tab 244 may be attached to the positive electrode collector 241 using the previously-described pressure sensitive adhesive sheet for batteries 1, and the electrode lead-out tab 244 can thereby be electrically connected to the positive electrode collector 241. The electrode lead-out tab 244 may be electrically connected also to the above positive electrode terminal 22. The negative electrode collector 242 may be electrically connected to the negative electrode terminal 23 via an electrode lead-out tab which is not illustrated.

In general, the positive electrode collector 241 and the negative electrode collector 242 may be made of a material of metal such as aluminum while the electrode lead-out tab 244 may be made of a material of metal such as aluminum and copper.

The electrolyte solution used in the lithium-ion battery 2 may ordinarily be a nonaqueous electrolyte solution. Preferred examples of the nonaqueous electrolyte solution include those in which a lithium salt as the electrolyte is dissolved in a mixed solvent of a cyclic carbonate and a lower chain carbonate. Examples of the lithium salt to be used include fluorine-based complex salts, such as lithium hexafluorophosphate (LiPF₆) and lithium borofluoride (LiBF₄), and LiN(SO₂Rf)₂.LiC(SO₂Rf)₃ (where Rf═CF₃, C₂F₅). Examples of the cyclic carbonate to be used include ethylene carbonate and propylene carbonate. Preferred examples of the lower chain carbonate include dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

The lithium-ion battery 2 according to the present embodiment can be manufactured by an ordinary method except that the previously-described pressure sensitive adhesive sheet for batteries 1 is used for fixation of the electrode lead-out tab 244.

In the lithium-ion battery 2 according to the present embodiment, the electrode lead-out tab 244 is attached to the positive electrode collector 241 using the pressure sensitive adhesive sheet for batteries 1. Owing to having the hard coat layer 12 obtained using a metal oxide sol, the pressure sensitive adhesive sheet for batteries 1 can be excellent in the insulation properties in an ordinary time, in a case of being heated to high temperatures (in a case in which matrices and the like of the base material 11, pressure sensitive adhesive layer 13, and hard coat layer 12 are carbonized), and further in a case of being immersed in an electrolyte solution for a long time and then heated to high temperatures.

As will be understood from the above, the lithium-ion battery 2 according to the present embodiment, in which the performance degradation, erroneous operation, thermal runaway, and short circuit due to the pressure sensitive adhesive sheet can be suppressed, is expected to be highly reliable as a battery and have excellent temperature stability and safety even under large-current conditions.

It should be appreciated that the embodiments heretofore explained are described to facilitate understanding of the present invention and are not described to limit the present invention. It is therefore intended that the elements disclosed in the above embodiments include all design changes and equivalents to fall within the technical scope of the present invention.

For example, in the pressure sensitive adhesive sheet for batteries 1, the release sheet 14 may be omitted. In an embodiment, the pressure sensitive adhesive sheet for batteries 1 may be provided with one or more other layers between the base material 11 and the hard coat layer 12 or between the hard coat layer 12 and the pressure sensitive adhesive layer 13.

EXAMPLES

Hereinafter, the present invention will be described further specifically with reference to examples, etc., but the scope of the present invention is not limited to these examples, etc.

Example 1 1. Formation of Hard Coat Layer on Base Material

A coating liquid for hard coat layer was prepared through mixing 25 mass parts of dipentaerythritol hexaacrylate (a material of which the glass-transition point is not observed after curing) as an active energy ray-curable component, 5 mass parts of hydroxycyclohexyl phenyl ketone as a photopolymerization initiator, and 75 mass parts (solid content equivalent, here and hereinafter) of a zirconia sol (average particle diameter of 15 nm) as a metal oxide sol and diluting them with methyl ethyl ketone. The volume ratio of the above dipentaerythritol hexaacrylate and zirconia sol was 65:35 (100:54).

One surface of a polyimide film (available from DU PONT-TORAY CO., LTD., trade name “Kapton 100H,” thickness of 25 μm, flame retardation level V-0 according to the UL94 standard) as a base material was coated with the above coating liquid using a knife coater and the coating liquid was then dried at 70° C. for 1 minute. Subsequently, the coating film was irradiated with ultraviolet rays (illuminance of 230 mW/cm², light amount of 510 mJ/cm²) to cure the coating film. A first laminate was thus obtained in which a hard coat layer having a content of metal oxide particles of 0.7 cm³/m² and a thickness of 2 μm was formed on one surface of the base material.

2. Formation of Coating Film of Pressure Sensitive Adhesive Composition on Release Sheet

A (meth)acrylic ester polymer was prepared using a solution polymerization method to copolymerize 76.8 mass parts of butyl acrylate, 19.2 mass parts of methyl acrylate, and 4 mass parts of acrylic acid. The molecular weight of this polymer was measured using gel permeation chromatography (GPC), which will be described later. The weight-average molecular weight (Mw) was 1,000,000.

Then, a coating liquid of a pressure sensitive adhesive composition was prepared through mixing 100 mass parts of the obtained (meth)acrylic ester polymer, 0.31 mass parts of aluminum tris(acetylacetonate) (available from Soken Chemical & Engineering Co., Ltd., trade name “M-5A”) as a metal chelate-based crosslinker, 2.35 mass parts of trimethylolpropane-modified tolylene diisocyanate (available from TOYOCHEM CO., LTD., trade name “BHS8515”) as an isocyanate-based crosslinker, and 0.5 mass parts of 3-glycidoxypropylmethyldimethoxysilane (available from Shin-Etsu Chemical Co., Ltd., trade name “KBM-403”) as a silane coupling agent and diluting them with methyl ethyl ketone.

A release sheet (available from LINTEC Corporation, trade name “PET251130”) was prepared in which one surface of a polyethylene terephthalate film was subjected to release treatment using a silicone-based release agent. The release-treated surface of the release sheet was coated with the obtained coating liquid using a knife coater and the coating liquid was then heat-treated at 120° C. for 1 minute. A second laminate was thus obtained in which the coating film of the pressure sensitive adhesive composition was laminated on the release-treated surface of the release sheet.

3. Production of Pressure Sensitive Adhesive Sheet for Batteries

The surface of the first laminate, produced as the above, at the side of the hard coat layer and the surface of the second laminate, produced as the above, at the side of the coating film of the pressure sensitive adhesive composition were attached to each other and they were then aged at 23° C. and 50% RH for 7 days. A pressure sensitive adhesive sheet for batteries was thus obtained in which the coating film of the pressure sensitive adhesive composition became the pressure sensitive adhesive layer. The thickness of the pressure sensitive adhesive layer was 7 μm. The thickness of the pressure sensitive adhesive layer was calculated through obtaining the total thickness of the pressure sensitive adhesive sheet for batteries and subtracting the thicknesses of the first laminate and the above release sheet from the total thickness.

Here, the gel fraction of the pressure sensitive adhesive constituting the pressure sensitive adhesive layer of the obtained pressure sensitive adhesive sheet for batteries due to immersion in an electrolyte solvent was measured as below.

The surface of the above second laminate at the side of the coating film of the pressure sensitive adhesive composition was attached to the release-treated surface of another release sheet (available from LINTEC Corporation, trade name “PET251130”) in which one surface of a polyethylene terephthalate film was subjected to release treatment using a silicone-based release agent. Thereafter, aging at 23° C. and 50% RH for 7 days was performed and a sheet for measurement was thus obtained comprising the pressure sensitive adhesive layer alone, of which both surfaces were protected by the release sheets.

The obtained sheet for measurement was cut into a size of 80 mm×80 mm and the release sheets protecting both surfaces of the pressure sensitive adhesive layer were removed. The pressure sensitive adhesive layer was wrapped with a polyester mesh (mesh size of 200) and the total mass was weighed using a precision balance. The mass of the pressure sensitive adhesive alone was calculated by subtracting the mass of the above mesh alone from the total mass. The calculated mass is represented by M1. Then, the pressure sensitive adhesive wrapped with the above polyester mesh was immersed in a prepared liquid as the electrolyte solvent at 80° C. for 72 hours. The prepared liquid was obtained by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 1:1. Thereafter, the pressure sensitive adhesive layer was taken out and once immersed in ethanol to dissolve and remove the attached electrolyte solvent, air-dried for 24 hours under an environment of a temperature of 23° C. and a relative humidity of 50%, and further dried in an oven at 80° C. for hours. After drying, the mass was weighed using a precision balance and the mass of the pressure sensitive adhesive alone was calculated by subtracting the mass of the above mesh alone. The calculated mass is represented by M2. The gel fraction (%) was calculated from the calculation formula of (M2/M1)×100. As a result, the gel fraction of the pressure sensitive adhesive due to immersion in the electrolyte solvent was 72%.

Example 2

A coating liquid for hard coat layer was prepared through mixing 30 mass parts of dipentaerythritol hexaacrylate (a material of which the glass-transition point is not observed after curing) as an active energy ray-curable component, 5 mass parts of hydroxycyclohexyl phenyl ketone as a photopolymerization initiator, and 70 mass parts of an alumina sol (average particle diameter of 15 nm) as a metal oxide sol and diluting them with methyl ethyl ketone. The volume ratio of the above dipentaerythritol hexaacrylate and alumina sol was 60:40 (≈100:67). The obtained coating liquid for hard coat layer was used to perform a process in the same manner as in Example 1 thereby to form a hard coat layer having a content of metal oxide particles of 0.8 cm³/m² and a thickness of 2 μm on one surface of the base material. Thereafter, a pressure sensitive adhesive sheet for batteries was manufactured in the same manner as in Example 1.

Example 3

A coating liquid for hard coat layer was prepared through mixing 22 mass parts of dipentaerythritol hexaacrylate (a material of which the glass-transition point is not observed after curing) as an active energy ray-curable component, 5 mass parts of hydroxycyclohexyl phenyl ketone as a photopolymerization initiator, and 78 mass parts of an alumina sol (average particle diameter of 15 nm) and diluting them with methyl ethyl ketone. The volume ratio of the above dipentaerythritol hexaacrylate and alumina sol was 50:50 (100:100). The obtained coating liquid for hard coat layer was used to perform a process in the same manner as in Example 1 thereby to form a hard coat layer having a content of metal oxide particles of 1.9 cm³/m² and a thickness of 3.8 μm on one surface of the base material. Thereafter, a pressure sensitive adhesive sheet for batteries was manufactured in the same manner as in Example 1.

Example 4

A coating liquid for hard coat layer was prepared through mixing 70 mass parts of dipentaerythritol hexaacrylate (a material of which the glass-transition point is not observed after curing) as an active energy ray-curable component, 5 mass parts of hydroxycyclohexyl phenyl ketone as a photopolymerization initiator, and 30 mass parts of an alumina sol (average particle diameter of 15 nm) and diluting them with methyl ethyl ketone. The volume ratio of the above dipentaerythritol hexaacrylate and alumina sol was 90:10 (100:11). The obtained coating liquid for hard coat layer was used to perform a process in the same manner as in Example 1 thereby to form a hard coat layer having a content of metal oxide particles of 0.27 cm³/m² and a thickness of 2.7 μm on one surface of the base material. Thereafter, a pressure sensitive adhesive sheet for batteries was manufactured in the same manner as in Example 1.

Comparative Example 1

A coating liquid for hard coat layer was prepared through mixing 40 mass parts of dipentaerythritol hexaacrylate (a material of which the glass-transition point is not observed after curing) as an active energy ray-curable component, 5 mass parts of hydroxycyclohexyl phenyl ketone as a photopolymerization initiator, and 60 mass parts of an organosilica sol (average particle diameter of 30 nm) and diluting them with methyl ethyl ketone. The volume ratio of the above dipentaerythritol hexaacrylate and organosilica sol was 55:45 (100:82). The obtained coating liquid for hard coat layer was used to perform a process in the same manner as in Example 1 thereby to form a hard coat layer having a content of particles of 0.9 cm³/m² and a thickness of 2 μm on one surface of the base material. Thereafter, a pressure sensitive adhesive sheet for batteries was manufactured in the same manner as in Example 1.

Comparative Example 2

A pressure sensitive adhesive sheet for batteries was produced in the same manner as in Example 1 except that the pressure sensitive adhesive layer on the release sheet was laminated directly on the base material without forming a hard coat layer on the base material.

Here, the previously-described weight-average molecular weight (Mw) refers to a weight-average molecular weight that is measured as a standard polystyrene equivalent value under the following condition using gel permeation chromatography (GPC) (GPC measurement).

<Measurement Condition>

GPC measurement apparatus: HLC-8020 available from Tosoh Corporation

GPC columns (passing in the order below): available from Tosoh Corporation

-   -   TSK guard column HXL-H     -   TSK gel GMHXL (×2)     -   TSK gel G2000HXL

Solvent for measurement: tetrahydrofuran

Measurement temperature: 40° C.

<Exemplary Test 1> (Steel Wool Resistance Test)

A steel wool resistance test was conducted for the hard coat layer of the first laminate obtained when producing the pressure sensitive adhesive sheet for batteries of each of Examples and Comparative Examples. The surface of the hard coat layer was rubbed at a load of 250 g/cm² using #0000 steel wool to reciprocate it ten times within a length of 10 cm and evaluated in accordance with the criteria below. Results are listed in Table 1.

∘: No line-like scratches were observed.

x: Line-like scratches were observed.

<Exemplary Test 2> (Measurement of Adhesive Strength)

The adhesive strength of the pressure sensitive adhesive sheet for batteries in this exemplary test was measured in accordance with JIS 20237: 2009 except the following operation.

The pressure sensitive adhesive sheet for batteries obtained in each of Examples and Comparative Examples was cut into a width of 25 mm and a length of 250 mm and the release sheet was then removed to obtain a test piece. The exposed pressure sensitive adhesive layer of the test piece was attached to an aluminum plate as an adherend using a rubber roller of 2 kg under an environment of 23° C. and 50% RH. Immediately thereafter, the test piece was peeled off from the above aluminum plate at a peel angle of 180° and a peel speed of 300 mm/min using a universal tensile tester (available from ORIENTEC Co., LTD., trade name “TENSILON UTM-4-100”) and the adhesive strength (N/25 mm) was thus measured. Results are listed in Table 1.

<Exemplary Test 3> (Evaluation of Insulation Properties in Normal Time)

The release sheet was removed from the pressure sensitive adhesive sheet for batteries obtained in each of Examples and Comparative Examples, the exposed pressure sensitive adhesive layer was attached to an aluminum plate (thickness: 1 mm), and this was used as a test piece. Using a circuit tester (available from HIOKI E.E. CORPORATION, trade name “Digital HiTester 3802-50”), the resistance value in the thickness direction of the pressure sensitive adhesive sheet for batteries was measured by bringing terminals of the circuit tester into contact with the pressure sensitive adhesive sheet for batteries located at a surface of the test piece and the aluminum plate located at the other surface of the test piece. On the basis of the resistance value in the thickness direction, the insulation properties of the pressure sensitive adhesive sheet for batteries in an ordinary time were evaluated in accordance with the criteria below. Results are listed in Table 1.

∘: The resistance value in the thickness direction of the pressure sensitive adhesive sheet for batteries was 1.0×10¹⁰Ω or higher.

x: The resistance value in the thickness direction of the pressure sensitive adhesive sheet for batteries was lower than 1.0×10¹⁰Ω.

<Exemplary Test 4> (Evaluation of Insulation Properties after High-Temperature Heating)

The test piece obtained in the same manner as in Exemplary Test 3 was heated under a nitrogen atmosphere at 800° C. for 1 hour. Thereafter, the resistance value in the thickness direction of the pressure sensitive adhesive sheet for batteries was measured in the same manner as in Exemplary Test 3. On the basis of the resistance value in the thickness direction, the insulation properties of the pressure sensitive adhesive sheet for batteries after high-temperature heating were evaluated in accordance with the criteria below. Results are listed in Table 1.

∘: The resistance value in the thickness direction of the pressure sensitive adhesive sheet for batteries was 1.0×10¹⁰Ω or higher.

x: The resistance value in the thickness direction of the pressure sensitive adhesive sheet for batteries was lower than 1.0×10¹⁰Ω.

<Exemplary Test 5> (Evaluation of Insulation Properties after Resistance to Electrolyte Solution and after Subsequent High-Temperature Heating)

The test piece obtained in the same manner as in Exemplary Test 3 was enclosed in an aluminum laminated bag together with a prepared liquid as an electrolyte solution obtained through mixing ethylene carbonate and diethyl carbonate at a volume ratio of 1:1 to make a mixture liquid and dissolving lithium hexafluorophosphate (LiPF₆) in the mixture liquid at a concentration of 1 mol/L, and they were heated under an environment of 80° C. for 4 weeks (electrolyte solution resistance test). Thereafter, the resistance value in the thickness direction of the pressure sensitive adhesive sheet for batteries (after resistance to electrolyte solution) was measured in the same manner as in Exemplary Test 3.

In addition, after the above electrolyte solution resistance test, the test piece was heated in the same manner as in Exemplary Test 4. Thereafter, the resistance value in the thickness direction of the pressure sensitive adhesive sheet for batteries (after electrolyte solution resistance test and subsequent high-temperature heating) was measured in the same manner as in Exemplary Test 3.

On the basis of the above resistance values in the thickness direction, the insulation properties of the pressure sensitive adhesive sheet for batteries after resistance to the electrolyte solution and after the subsequent high-temperature heating (after electrolyte solution resistance test and subsequent high-temperature heating) were evaluated in accordance with the criteria below. Results are listed in Table 1.

∘: The resistance value in the thickness direction of the pressure sensitive adhesive sheet for batteries was 1.0×10¹⁰Ω or higher.

x: The resistance value in the thickness direction of the pressure sensitive adhesive sheet for batteries was lower than 1.0×10¹⁰Ω.

<Exemplary Test 6> (Evaluation of Hard Coat Layer after Electrolyte Solution Resistance Test)

The release sheet was removed from the pressure sensitive adhesive sheet for batteries obtained in each of Examples and Comparative Examples, the exposed pressure sensitive adhesive layer was attached to an aluminum plate (thickness: 1 mm), and this was used as a test piece. The obtained test piece was enclosed in an aluminum laminated bag together with a prepared liquid obtained through mixing ethylene carbonate and diethyl carbonate at a volume ratio of 1:1 to make a mixture liquid and dissolving lithium hexafluorophosphate (LiPF₆) in the mixture liquid at a concentration of 1 mol/L, and they were heated under an environment of 80° C. for 4 weeks.

Thereafter, the pressure sensitive adhesive sheet for batteries was released from the aluminum plate and X-ray analysis was performed for a cross section of the pressure sensitive adhesive sheet for batteries using an energy dispersive X-ray spectroscope (EDX; available from AMETEK Co., Ltd., trade name “Energy Dispersive X-ray Analyzer Genesis Series Standard”). The presence or absence of peaks of inorganic elements (Zr, Al, Si) added to the hard coat layer was confirmed, and the hard coat layer after the electrolyte solution resistance test was evaluated (escapability of inorganic particles). Results are listed in Table 1.

∘: Peaks of inorganic elements were present.

x: Peaks of inorganic elements were absent.

TABLE 1 Evaluation of insulation properties Evaluation after resistance to Evaluation Evaluation of electrolyte solution of hard coat of insulation and after subsequent layer after insulation properties high-temperature electrolyte Steel wool Adhesive properties after high- heating solution resistance strength in ordinary temperature After resistance → resistance test (N/25 mm) time heating After heating test Example 1 ◯ 3.0 ◯ ◯ ◯→◯ ◯ Example 2 ◯ 3.0 ◯ ◯ ◯→◯ ◯ Example 3 ◯ 3.0 ◯ ◯ ◯→◯ ◯ Example 4 ◯ 3.0 ◯ ◯ ◯→◯ ◯ Comparative ◯ 3.0 ◯ ◯ ◯→X X Example 1 Comparative X 3.0 ◯ X ◯→X — Example 2

As apparent from Table 1, the pressure sensitive adhesive layers of the pressure sensitive adhesive sheets for batteries of Examples are excellent in the insulation properties in an ordinary time, in a case of being heated to high temperatures, in a case of being immersed in an electrolyte solution for a long time, and in a case of being immersed in the electrolyte solution for a long time and then heated to high temperatures. In the pressure sensitive adhesive sheet for batteries of Comparative Example 1, the inorganic particles (silica) in the hard coat layer appear to escape into the electrolyte solution due to immersion in the electrolyte solution thereby to deteriorate the insulation properties.

INDUSTRIAL APPLICABILITY

The pressure sensitive adhesive composition and the pressure sensitive adhesive sheet for batteries according to the present invention are suitable for attaching an electrode lead-out tab to an electrode inside a lithium-ion battery.

DESCRIPTION OF REFERENCE NUMERALS

-   1 . . . Pressure sensitive adhesive sheet for batteries -   11 . . . Base material -   12 . . . Hard coat layer -   13 . . . Pressure sensitive adhesive layer -   14 . . . Release sheet -   2 . . . Lithium-ion battery -   21 . . . Exterior body -   22 . . . Positive electrode terminal -   23 . . . Negative electrode terminal -   24 . . . Electrode body -   241 . . . Positive electrode collector -   241 a . . . Positive electrode active material layer -   242 . . . Negative electrode collector -   242 a . . . Negative electrode active material layer -   243 . . . Separator -   244 . . . Electrode lead-out tab 

1. A pressure sensitive adhesive sheet for batteries, comprising: a base material; a hard coat layer provided at one side of the base material; and a pressure sensitive adhesive layer provided at a side of the hard coat layer opposite to the base material, the hard coat layer being formed of a composition for hard coat layer that contains a metal oxide sol, the metal oxide sol being a sol of a metal oxide that has insulation properties.
 2. The pressure sensitive adhesive sheet for batteries as recited in claim 1, wherein the metal oxide sol is at least one type selected from a group consisting of an alumina sol, zirconia sol, and magnesia sol.
 3. The pressure sensitive adhesive sheet for batteries as recited in claim 1, wherein the composition for hard coat layer contains the metal oxide sol and an active energy ray-curable component.
 4. The pressure sensitive adhesive sheet for batteries as recited in claim 1, wherein the hard coat layer contains 0.01 cm³/m² or more and 7 cm³/m² or less of metal oxide particles originated from the metal oxide sol.
 5. A lithium-ion battery wherein two or more conductors are fixed in a state in which the two or more conductors are in contact with each other in the battery using the pressure sensitive adhesive sheet for batteries as recited in claim
 1. 